1. Field of the Invention
The present invention relates to improvements of a mechanical pencil of the type having a push-out mechanism or the type provided with a lead chuck.
A feature of the invention is the possibility of saving lead by minimizing the length of the broken piece remaining in the holding tube in case of lead breakage.
Another feature of the invention is a composition of a mechanical pencil whereby leads are safely retracted so as not to be broken. That is, excessive pushing force applied to the lead case is buffered by a buffer spring so as not to be transmitted to the leads and the chuck, thus retracting the lead by the chuck without breaking the lead by the chuck within the holder tube or the thin tube at the end of the holder tube.
2. Description of the Prior Art
A chuck 2 used in the conventional push-out type mechanical pencils and mechanical pencils having a chuck as shown in FIGS. 14 to 23 has a two-slitted or three-slitted chuck point 201, the length of which is normally approximately 2 mm. Therefore, if a lead is broken at the end of the chuck point 201 due to some cause, the broken piece remaining between the end of the chuck point 201 and the end of the holder tube 1 or the tip end of the thin tube 10 becomes unnecessarily long, thus causing the waste of the lead a.
A variety of mechanical pencils having a chuck, as shown in FIGS. 14 to 23, have been introduced. These conventional mechanical pencils are supposed to be free from lead breakage trouble in the retraction of the lead a within the holder tube 1, especially in the first example of FIGS. 14 and 15. However, even the mechanical pencil of this type is not satisfactory. In this first example, the lower part of a chucking point 201 of a chuck 2 is formed in the shape of a large tapered closing cone. Therefore, the chucking point 201 is closed suddenly to instantaneously fasten the lead a when the chucking point 201 starts engaging with a movable ring 7 (immediately before the state shown in FIG. 15), even though the mechanical pencil is provided with a buffer spring 6 and the bore of the movable ring 7 is tapered corresponding to the taper of the lower part of the chucking point 201. This sudden fastening causes the lead a to be broken at the tip end of the chucking point 201.
Finally the buffer spring 6 is compressed as shown in FIG. 15. The mechanical pencil is then used for writing in the state as shown in FIG. 15. However, the chucking point 201 is not held steadfastly as the mechanical pencil of this type has no fastening ring so that the alignment of the chucking point 201 with the holder tube 1 is liable to be distorted causing the lead a to be broken.
Referring to FIGS. 16 and 17, these Figures show a second example of a pencil not being constructed to buffer the fastening force applied to the lead a when the chucking point 201 of the chuck 2 engages with a movable ring 7. Here, the lead a is liable to be broken at the tip of the chucking point 201 so that the chuck point 201 retracts only a part of the lead within the holder tube 1. Thus, the second example cannot eliminate lead breakage.
Referring to FIGS. 18 and 19, a third example is shown which has a smaller movable ring 7 inserted in a larger intermediate movable ring 701 and a buffer spring 6 between an end of the intermediate movable ring 701 and the holder tube 1 and where the external shape of a chucking point 201 of a chuck 2 is formed in a small reverse tapered cone. In this example, when a chucking point 201 of a chuck 2 is pulled up by the strong force applied by a retraction spring 3 and starts engaging with movable ring 7 (immediately before the state as shown in FIG. 18), the chucking point 201 strikes against the internal edge of the movable ring 7 so that the chucking point 201 is suddenly closed to thereby break the lead a as described in the first example referring to FIGS. 14 and 15. Furthermore, the third example has another disadvantage in that the chucking point 201 carrying the lead a and engaging with the movable ring 7 causes the movable ring 7 to strike against a shoulder 103 when being pulled into retraction by the retraction spring 3 as shown in FIG. 18 and the shock caused to the chucking point 201 by the striking of the movable ring against the shoulder 103 often breaks the lead a.
Referring to FIGS. 20 and 21, a fourth example is shown. In this fourth example, a chucking point 201 carrying the lead a and engaging with a movable ring 7 also strikes the movable ring against a shoulder 103 to stop pulling movement by retraction spring 3 (movement from the state as shown in FIG. 21 to the state as shown in FIG. 20), and the shock caused by the striking of the movable ring against the shoulder 103 often breaks the lead a.
Referring to FIGS. 22 and 23, a fifth example is shown which also has a disadvantage similar to that of the fourth example. The fifth example has two movable rings 7 and 701. The upper movable ring 7 has a downwardly opening conical internal surface while the lower movable ring 701 has an upwardly opening conical internal surface. Although the upper surface of the chucking point 201 of the chuck 2 is shaped to fit exactly in the conical bore of the upper movable ring 7, the lead a is liable to be broken because the chucking point 201 of the chuck 2 is pulled upward by a strong retraction spring 3 from the position shown in FIG. 23 and first engages with the upper movable ring 7, then is pulled further together with the movable ring 7 until the upper movable ring 7 strikes severely against a shoulder 103. The lead a is often broken at the end of the chucking point 201 of the chuck 2 by the severe impact.
Various mechanisms for retracting the lead within the holder tube have been introduced as hereinbefore described in reference to FIGS. 14 to 23, however, none of these conventional mechanisms is effective in overcoming the disadvantage that the lead is often broken by the impulsive chucking applied by the chucking point when the chuck retracts. This disadvantage is conspicuous when thick but soft leads or hard but thin (0.5 mm to 0.2 mm in diameter) leads are used. This disadvantage is caused by the lack of a buffer mechanism which moderates the impact applied to the lead by the fastening action of the chucking point.